File: dither.c

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libaudio-flac-decoder-perl 0.3+dfsg-2
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/* plugin_common - Routines common to several plugins
 * Copyright (C) 2002,2003,2004  Josh Coalson
 *
 * dithering routine derived from (other GPLed source):
 * mad - MPEG audio decoder
 * Copyright (C) 2000-2001 Robert Leslie
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#include "include/common.h"
#include "include/dither.h"
#include "FLAC/assert.h"

/* 32-bit pseudo-random number generator
 *
 * @@@ According to Miroslav, this one is poor quality, the one from the
 * @@@ original replaygain code is much better
 */
static FLAC__INLINE FLAC__uint32 prng(FLAC__uint32 state)
{
	return (state * 0x0019660dL + 0x3c6ef35fL) & 0xffffffffL;
}

/* dither routine derived from MAD winamp plugin */

typedef struct {
	FLAC__int32 error[3];
	FLAC__int32 random;
} dither_state;

static FLAC__INLINE FLAC__int32 linear_dither(
	unsigned source_bps, unsigned target_bps, FLAC__int32 sample, 
	dither_state *dither, const FLAC__int32 MIN, const FLAC__int32 MAX) {

	unsigned scalebits;
	FLAC__int32 output, mask, random;

	FLAC__ASSERT(source_bps < 32);
	FLAC__ASSERT(target_bps <= 24);
	FLAC__ASSERT(target_bps <= source_bps);

	/* noise shape */
	sample += dither->error[0] - dither->error[1] + dither->error[2];

	dither->error[2] = dither->error[1];
	dither->error[1] = dither->error[0] / 2;

	/* bias */
	output = sample + (1L << (source_bps - target_bps - 1));

	scalebits = source_bps - target_bps;
	mask = (1L << scalebits) - 1;

	/* dither */
	random = (FLAC__int32)prng(dither->random);
	output += (random & mask) - (dither->random & mask);

	dither->random = random;

	/* clip */
	if (output > MAX) {
		output = MAX;

		if (sample > MAX) {
			sample = MAX;
		}

	} else if (output < MIN) {
		output = MIN;

		if (sample < MIN) {
			sample = MIN;
		}
	}

	/* quantize */
	output &= ~mask;

	/* error feedback */
	dither->error[0] = sample - output;

	/* scale */
	return output >> scalebits;
}

size_t pack_pcm_signed_big_endian(FLAC__byte *data, FLAC__int32 *input, 
	unsigned wide_samples, unsigned channels, unsigned source_bps, unsigned target_bps) {

	static dither_state dither[FLAC__MAX_SUPPORTED_CHANNELS];
	FLAC__byte * const start = data;
	FLAC__int32 sample;
	unsigned samples, channel;
	const unsigned bytes_per_sample = target_bps / 8;
	const unsigned incr = bytes_per_sample * channels;
	const FLAC__int32 MIN = -(1L << (source_bps - 1));
	const FLAC__int32 MAX = ~MIN; /*(1L << (source_bps-1)) - 1 */

	FLAC__ASSERT(channels > 0 && channels <= FLAC__MAX_SUPPORTED_CHANNELS);
	FLAC__ASSERT(source_bps < 32);
	FLAC__ASSERT(target_bps <= 24);
	FLAC__ASSERT(target_bps <= source_bps);
	FLAC__ASSERT((source_bps & 7) == 0);
	FLAC__ASSERT((target_bps & 7) == 0);

	for (channel = 0; channel < channels; channel++) {
		
		samples = wide_samples;
		data = start + bytes_per_sample * channel;

		while (samples--) {

			if (source_bps != target_bps) {
				sample = linear_dither(source_bps, target_bps, *input++, &dither[channel], MIN, MAX);
			} else {
				sample = *input++;
			}

			switch (target_bps) {
				case 8:
					data[0] = sample ^ 0x80;
					break;
				case 16:
					data[0] = (FLAC__byte)(sample >> 8);
					data[1] = (FLAC__byte)sample;
					break;
				case 24:
					data[0] = (FLAC__byte)(sample >> 16);
					data[1] = (FLAC__byte)(sample >> 8);
					data[2] = (FLAC__byte)sample;
					break;
			}

			data += incr;
		}
	}

	return wide_samples * channels * (target_bps/8);
}

size_t pack_pcm_signed_little_endian(FLAC__byte *data, FLAC__int32 *input, 
	unsigned wide_samples, unsigned channels, unsigned source_bps, unsigned target_bps) {

	static dither_state dither[FLAC__MAX_SUPPORTED_CHANNELS];
	FLAC__byte * const start = data;
	FLAC__int32 sample;
	unsigned samples, channel;
	const unsigned bytes_per_sample = target_bps / 8;
	const unsigned incr = bytes_per_sample * channels;
	const FLAC__int32 MIN = -(1L << (source_bps - 1));
	const FLAC__int32 MAX = ~MIN; /*(1L << (source_bps-1)) - 1 */

	FLAC__ASSERT(channels > 0 && channels <= FLAC__MAX_SUPPORTED_CHANNELS);
	FLAC__ASSERT(source_bps < 32);
	FLAC__ASSERT(target_bps <= 24);
	FLAC__ASSERT(target_bps <= source_bps);
	FLAC__ASSERT((source_bps & 7) == 0);
	FLAC__ASSERT((target_bps & 7) == 0);

	for (channel = 0; channel < channels; channel++) {
		samples = wide_samples;
		data = start + bytes_per_sample * channel;

		while (samples--) {

			if (source_bps != target_bps) {
				sample = linear_dither(source_bps, target_bps, *input++, &dither[channel], MIN, MAX);
			} else {
				sample = *input++;
			}

			switch(target_bps) {
				case 8:
					data[0] = sample ^ 0x80;
					break;
				case 24:
					data[2] = (FLAC__byte)(sample >> 16);
					/* fall through */
				case 16:
					data[1] = (FLAC__byte)(sample >> 8);
					data[0] = (FLAC__byte)sample;
			}

			data += incr;
		}
	}

	return wide_samples * channels * (target_bps/8);
}